A prominent businessman in Thailand has been ordered to attend court next month, after being caught in a wildlife park with soup made from a freshly killed rare black leopard.

Key points:

Premchai Karnasuta own a construction empire that built Bangkok's skytrain

Raid of his home also found tusks suspected to be from African elephants

Thought to be 900 to 2500 Indochinese black leopards left in the wild

Premchai Karnasuta is the owner of Italian-Thai Development, a construction empire that built the Suvarnabhumni International Airport and Bangkok's Skytrain.

Mr Premchai has been ordered to appear in court on March 26.

He and three others were found in the Thungyai Naresuan Wildlife Sanctuary on February 4 with rifles, and the carcasses of a rare black Indochinese leopard, a muntjac (deer) and a pheasant.

"The subspecies of the Indochinese black leopard is rare, there is an estimation of about 900 to 2,500 still left in the wild, of which only 11 per cent are black," said Edwin Wiek, founder of Wildlife Friends Foundation Thailand.

So in the worst-case scenario, the black leopard that was skinned and eaten in the World Heritage-listed sanctuary was one of the last 99.

Premchai Karnasuta told police he had permission to be in the park, but rangers deny arrangements were made for an illegal hunting party.

The tycoon was released on bail, but a subsequent raid of his home found tusks suspected to be from African elephants, as well as 40 rifles.

Ranger hailed a hero

The case has outraged Thais.

University students donned black leopard masks and held a candlelit vigil.

An image of a black cat shot through the head and weeping was painted on an Italian-Thai Development sign, with similar pictures trending on Twitter.

"Most Thai people seriously care about their natural heritage, their national parks, their wildlife and are just generally pissed off with rich people getting away with ugly things like this," Mr Wiek told the ABC.

"This case is a bit different because some of the rangers were making photographs from the beginning, some of the rangers didn't know who Premchai was.

"By then the black leopard was already found, pictures were being shared and I think there was a point of no return."

The ranger in charge of the bust — Wichien Chinnawong — has been hailed a hero for following procedure, despite leaked audio suggesting bribes were offered.

"I didn't think he would be some famous big CEO … but after arresting him, I'm not worried or scared of someone interfering in my work," the ranger said, as quoted in Khaosod English.

"When someone with money does something wrong and is arrested, they should be treated according to the law, the same as with any villager or any other citizens."

The lanky ranger has received support from high places.

"Fight on Khun Wichien Chinnawong" read an Instagram post from Princess Ubolratana, the eldest child of Queen Sirikit and the late King Bhumibol Adulyadej.

Echoes of 1973, when poaching felled a dictator

For older Thais, the case brought up memories of another incident in the same national park — one with huge political ramifications.

In 1973, during the dictatorship of Field Marshal Thanom Kittikachorn, there was a deadly helicopter crash in the Thungyai Naresuan park.

Six high-ranking soldiers and police died in the accident, but it was other corpses that sparked revolt.

"Dead bodies of endangered wildlife were scattered all over the area because they were all hunted, they fell down with the helicopter," Mr Wiek said.

It emerged that 50 officers were on a hunting party, along with businessmen and an actress, although they tried to pass it off as a "secret mission".

"The scandal channelled resistance to the arrogant military government at the time, helping to stoke anger which led to the historical political uprising of October 14, 1973," wrote the Bangkok Post this week.